Which term defines the tightest possible fit between two mating parts?

Which term defines the tightest possible fit between two mating parts?

• A. Clearance Fit
• B. Allowance
• C. Interference
• D. Parts List

Answer: (B)

When two parts are designed to mate, engineers use tolerances to control how snugly they fit. The categories usually described are clearance, transition, and interference fits. A clearance fit leaves some space between the parts, so they can move relative to each other; this is the loosest common scenario. The tightest possible fit occurs when the parts actually overlap in size so there is no room for movement—the assembly requires force to bring the parts together. This is called an interference fit, often used for press fits where a shaft is pressed into a hub or a bearing is pressed into a housing. The difference between the hole and shaft sizes that designers plan is the allowance, which can be positive (leading to clearance) or negative (leading to interference) depending on the desired fit. A parts list is simply a document describing components, not a fit type.

When two parts are designed to mate, engineers use tolerances to control how snugly they fit. The categories usually described are clearance, transition, and interference fits. A clearance fit leaves some space between the parts, so they can move relative to each other; this is the loosest common scenario. The tightest possible fit occurs when the parts actually overlap in size so there is no room for movement—the assembly requires force to bring the parts together. This is called an interference fit, often used for press fits where a shaft is pressed into a hub or a bearing is pressed into a housing. The difference between the hole and shaft sizes that designers plan is the allowance, which can be positive (leading to clearance) or negative (leading to interference) depending on the desired fit. A parts list is simply a document describing components, not a fit type.